1. Field of the Invention
The invention relates to a process for the removal of nitrogen oxides and soot from exhaust gases of machines and combustion installations burning heavy fuel oil by means of free-passage catalysts at increased temperatures, with the addition of ammonia into the exhaust gas stream ahead of the catalysts.
2. Description of the Prior Art
Exhaust gases from machines burning heavy fuel oil or installations in which heavy fuel oil is burned contain significant quantities of nitrogen oxides and soot (Bacherach 5-7). Nitrogen oxides, for example, have been removed from flue gases since about 1965 by means of an iron oxide chromium oxide catalyst, with the addition of appropriate amounts of ammonia. The temperatures at the catalyst are approximately 280.degree. C. to 350.degree. C. It has been shown that soot particles thereby accumulate on the catalyst, and over time, the catalysts become clogged. Even when bulk catalysts are used, there is a residual clogging, in spite of the burn-off of the soot, because the soot from heavy fuel oils is contaminated with non-combustible ingredients, for example, vanadium pentoxide, nickel oxide, ash, etc. These ingredients inevitably clog the catalyst bed, so that the desired removal of nitrogen oxides is adversely affected.